1. Field of the disclosure
The present disclosure relates to a light source device including an excitation light source and a fluorescence light-emitting plate, and to a projection type display apparatus employing this light source device.
2. Description of the Prior Art
In recent years, various kinds of apparatuses are proposed for projection type display apparatuses in which light emitted from a light source is condensed onto an image display device such as a DMD (Digital Mirror Device) and a liquid crystal device so that a color image is projected onto a screen.
The light source of one of the projection type display apparatuses having been proposed is constructed from: a semiconductor light-emitting element like a light-emitting diode and a semiconductor laser; and a fluorescence light-emitting plate onto which excitation light from the semiconductor light-emitting element is projected so that fluorescence emission light is emitted.
In such projection type display apparatuses, for the purpose of realizing display of a high luminance image on a large screen, efforts are being made for luminance enhancement in the light sources (for example, see Japanese Laid-Open Patent Publication No. 2011-53320).
In the conventional projection type display apparatus disclosed in Japanese Laid-Open Patent Publication No. 2011-53320, the weight density content of green phosphor in the fluorescent substance layer and the film thickness of the layer are set at predetermined values so that the light emission intensity of the fluorescence emission light is enhanced.
In the fluorescence light-emitting region of the projection type display apparatus of Japanese Laid-Open Patent Publication No. 2011-53320, a reflecting surface is formed on the surface of a metallic material or the like by silver vapor deposition or the like. Then, a transparent protective film of magnesium fluoride or the like is formed on the surface of the reflecting surface by spattering. Further, a green phosphor layer is provided on the surface of the protective film. That is, the fluorescence light-emitting region of Japanese Laid-Open Patent Publication No. 2011-53320 indicates a configuration that a protective film of magnesium fluoride or the like and a reflecting surface of silver or the like are formed under a green phosphor layer.
For the purpose of improving utilization of reflected light in the fluorescence light-emitting region, further improvement in the reflectivity is effective. The configuration of the reflecting surface of silver provides a relative reflectivity of approximately 95%. However, a configuration is desired that a still higher reflectivity is achieved so that an interface loss between the fluorescent substance layer and the substrate is reduced. Nevertheless, in the configuration employing silver, a limitation in the physical properties of silver itself causes difficulty in further improvement of the reflectivity.
Further, in the case of the reflecting surface formed by vapor deposition of silver, the use of silver which is an expensive metal causes a disadvantage in the cost. Further, preparation processing for the substrate is necessary for ensuring the flatness and the surface roughness of the substrate, and hence another disadvantage is caused in the cost. Further, a possibility arises that when high luminance excitation light is projected, heat is generated and causes thermal oxidation of silver. Silver has unsatisfactory light resistance and moisture resistance and need be avoided from thermal oxidation. Thus, a dense and pinhole-free protective film is necessary and a disadvantage is caused in the cost.
As such, the reflecting surface employing silver has problems that its physical properties cause a limitation in improvement of the reflectivity and that cost reduction is difficult.